Preheat oven to 350 degrees. Grease a 9x13 Pyrex dish with non-stick spray.
Prepare brownie mix according to package instructions. Add peanut butter chips.
Bake for 20-25 minutes (do not over bake).
Cut peanut butter cups in half and set aside.
In a large bowl, mix instant vanilla pudding and 4 cups of milk. Allow pudding time to soft-set (usually about 5 minutes).
After pudding is firm, whisk in peanut butter and vanilla and mix well.
Fold in 1 1/2 tubs of Cool Whip and mix well.
Cut cooled brownies into squares. Assemble brownies, pudding, peanut butter cups and 1 1/2 tubs of Cool Whip.
Begin layering process by starting with brownies, pudding, Cool Whip and peanut butter cups.
Repeat (will be enough ingredients for 3 layers).
Top with peanut butter cups for garnish.